Professor John O'Keefe speaks at a news conference in London October 6, 2014. Anglo-American John O'Keefe and Norwegian couple May-Britt and Edvard Moser won the 2014 Nobel Prize for medicine on Monday for discovering the brain's internal positioning system, helping humans find their way and giving clues to how strokes and Alzheimer's affect the brain. REUTERS/Suzanne Plunkett (BRITAIN - Tags: SCIENCE TECHNOLOGY SOCIETY HEALTH) 

Professor John O'Keefe smiles as he arrives at a news conference in London October 6, 2014. Anglo-American John O'Keefe and Norwegian couple May-Britt and Edvard Moser won the 2014 Nobel Prize for medicine on Monday for discovering the brain's internal positioning system, helping humans find their way and giving clues to how strokes and Alzheimer's affect the brain. REUTERS/Suzanne Plunkett (BRITAIN - Tags: SCIENCE TECHNOLOGY SOCIETY HEALTH TPX IMAGES OF THE DAY) 

Professor John O'Keefe listens to a question during a news conference in London October 6, 2014. Anglo-American John O'Keefe and Norwegian couple May-Britt and Edvard Moser won the 2014 Nobel Prize for medicine on Monday for discovering the brain's internal positioning system, helping humans find their way and giving clues to how strokes and Alzheimer's affect the brain. REUTERS/Suzanne Plunkett (BRITAIN - Tags: SCIENCE TECHNOLOGY SOCIETY HEALTH) 

Professor John O'Keefe speaks at a news conference in London October 6, 2014. Anglo-American John O'Keefe and Norwegian couple May-Britt and Edvard Moser won the 2014 Nobel Prize for medicine on Monday for discovering the brain's internal positioning system, helping humans find their way and giving clues to how strokes and Alzheimer's affect the brain. REUTERS/Suzanne Plunkett (BRITAIN - Tags: SCIENCE TECHNOLOGY SOCIETY HEALTH) 

Professor John O'Keefe walks back to his office at University College London (UCL), in London October 6, 2014. Anglo-American John O'Keefe and Norwegian couple May-Britt and Edvard Moser won the 2014 Nobel Prize for medicine on Monday for discovering the brain's internal positioning system, helping humans find their way and giving clues to how strokes and Alzheimer's affect the brain. REUTERS/Suzanne Plunkett (BRITAIN - Tags: SCIENCE TECHNOLOGY SOCIETY HEALTH EDUCATION) 

Professor John O'Keefe poses in his laboratory at University College London (UCL), in London October 6, 2014. Anglo-American John O'Keefe and Norwegian couple May-Britt and Edvard Moser won the 2014 Nobel Prize for medicine on Monday for discovering the brain's internal positioning system, helping humans find their way and giving clues to how strokes and Alzheimer's affect the brain. REUTERS/Suzanne Plunkett (BRITAIN - Tags: SCIENCE TECHNOLOGY SOCIETY HEALTH) 

Professor John O'Keefe smiles as he poses at University College London in London October 6, 2014. Anglo-American John O'Keefe and Norwegian couple May-Britt and Edvard Moser won the 2014 Nobel Prize for medicine on Monday for discovering the brain's internal positioning system, helping humans find their way and giving clues to how strokes and Alzheimer's affect the brain. REUTERS/Suzanne Plunkett (BRITAIN - Tags: SCIENCE TECHNOLOGY SOCIETY)

Professor John O'Keefe smiles as he poses at University College London in London October 6, 2014. Anglo-American John O'Keefe and Norwegian couple May-Britt and Edvard Moser won the 2014 Nobel Prize for medicine on Monday for discovering the brain's internal positioning system, helping humans find their way and giving clues to how strokes and Alzheimer's affect the brain. REUTERS/Suzanne Plunkett (BRITAIN - Tags: SCIENCE TECHNOLOGY SOCIETY)

Professor John O'Keefe answers a question during a news conference in London October 6, 2014. Anglo-American John O'Keefe and Norwegian couple May-Britt and Edvard Moser won the 2014 Nobel Prize for medicine on Monday for discovering the brain's internal positioning system, helping humans find their way and giving clues to how strokes and Alzheimer's affect the brain. REUTERS/Suzanne Plunkett (BRITAIN - Tags: SCIENCE TECHNOLOGY SOCIETY HEALTH TPX IMAGES OF THE DAY) 

Professor John O'Keefe listens to a question during a news conference in London October 6, 2014. Anglo-American John O'Keefe and Norwegian couple May-Britt and Edvard Moser won the 2014 Nobel Prize for medicine on Monday for discovering the brain's internal positioning system, helping humans find their way and giving clues to how strokes and Alzheimer's affect the brain. REUTERS/Suzanne Plunkett (BRITAIN - Tags: SCIENCE TECHNOLOGY SOCIETY HEALTH) 

Professor John O'Keefe (R) laughs with Science Media Centre Chief Executive, Fiona Fox, during a news conference in London October 6, 2014. Anglo-American John O'Keefe and Norwegian couple May-Britt and Edvard Moser won the 2014 Nobel Prize for medicine on Monday for discovering the brain's internal positioning system, helping humans find their way and giving clues to how strokes and Alzheimer's affect the brain. REUTERS/Suzanne Plunkett (BRITAIN - Tags: SCIENCE TECHNOLOGY SOCIETY HEALTH) 

Professor John O'Keefe (C) walks along Euston Road on his way to a news conference in London October 6, 2014. Anglo-American John O'Keefe and Norwegian couple May-Britt and Edvard Moser won the 2014 Nobel Prize for medicine on Monday for discovering the brain's internal positioning system, helping humans find their way and giving clues to how strokes and Alzheimer's affect the brain. REUTERS/Suzanne Plunkett (BRITAIN - Tags: SCIENCE TECHNOLOGY SOCIETY HEALTH) 

Scientist Edvard Moser of Norway poses inside Max Planck Institute Martinsried of Biochemistry and Neurobiology in Munich, October 6, 2014. British-American John O'Keefe and Norwegians May-Britt and Moser won the 2014 Nobel Prize for medicine for discovering the brain's navigation system and giving clues as to how strokes and Alzheimer's disrupt it. REUTERS/Michaela Rehle (GERMANY - Tags: HEALTH SCIENCE TECHNOLOGY) 

Scientist Edvard Moser of Norway poses inside Max Planck Institute Martinsried of Biochemistry and Neurobiology in Munich, October 6, 2014. British-American John O'Keefe and Norwegians May-Britt and Moser won the 2014 Nobel Prize for medicine for discovering the brain's navigation system and giving clues as to how strokes and Alzheimer's disrupt it. REUTERS/Michaela Rehle (GERMANY - Tags: HEALTH SCIENCE TECHNOLOGY) 

Scientist Edvard Moser of Norway receives a call inside Max Planck Institute Martinsried of Biochemistry and Neurobiology in Munich, October 6, 2014. British-American John O'Keefe and Norwegians May-Britt and Moser won the 2014 Nobel Prize for medicine for discovering the brain's navigation system and giving clues as to how strokes and Alzheimer's disrupt it. REUTERS/Michaela Rehle (GERMANY - Tags: HEALTH SCIENCE TECHNOLOGY) 

Scientist Edvard Moser of Norway poses inside Max Planck Institute Martinsried of Biochemistry and Neurobiology in Munich, October 6, 2014. British-American John O'Keefe and Norwegians May-Britt and Moser won the 2014 Nobel Prize for medicine for discovering the brain's navigation system and giving clues as to how strokes and Alzheimer's disrupt it. REUTERS/Michaela Rehle (GERMANY - Tags: HEALTH SCIENCE TECHNOLOGY) 

Scientist Edvard Moser of Norway poses inside Max Planck Institute Martinsried of Biochemistry and Neurobiology in Munich, October 6, 2014. British-American John O'Keefe and Norwegians May-Britt and Moser won the 2014 Nobel Prize for medicine for discovering the brain's navigation system and giving clues as to how strokes and Alzheimer's disrupt it. REUTERS/Michaela Rehle (GERMANY - Tags: HEALTH SCIENCE TECHNOLOGY) 

Scientist Edvard Moser of Norway poses inside Max Planck Institute Martinsried of Biochemistry and Neurobiology in Munich, October 6, 2014. British-American John O'Keefe and Norwegians May-Britt and Moser won the 2014 Nobel Prize for medicine for discovering the brain's navigation system and giving clues as to how strokes and Alzheimer's disrupt it. REUTERS/Michaela Rehle (GERMANY - Tags: HEALTH SCIENCE TECHNOLOGY) 

NOBEL-PRIZE MEDICINE - Chart and timeline showing breakdown of past Nobel laureates in Physiology or Medicine by country of origin. Includes details of the winner of the 2014 prize. (SIN06)